A major concern in drilling wells is that the lining of the shaft (the “casing”) has the potential to collapse or rupture. When drilling a well, individual lengths of tubes often are secured together to form a casing string. Each section of the casing string may be cemented within the wellbore before a next smaller diameter portion is drilled and cased. The concentric casings form annuli which may or may not extend the full length of the well. Fluids, often referred to as spacer fluid or drilling fluid, typically are inserted between the top of the cement and the wellhead within the annular spaces. When these fluids are heated by oil pumped from deep within the ground and having a relatively high temperature, thermal expansion can create high pressures in the spacer fluid and result in collapse or rupture of the casing. This is commonly known as “annular pressure buildup.” When this occurs, the well may become inoperable and another well must be drilled at a significant cost. In addition, contaminants may be leaked into the environment.
One solution to this problem is described in U.S. Patent Application 2007/0114033 (Hermes et al.), which describes a spacer fluid that decreases in volume as the temperature of the fluid is increased, thus reducing pressure build-up as high-temperature oil is pumped through the production tubing. The spacer fluid comprises a monomer which undergoes polymerization and decreases the volume of the fluid as the reaction proceeds. Just prior to inserting the spacer fluid into the well, the proper amount of initiator is added. Thus, it is of critical importance to know the amount of the monomer in the fluid, both at the time of mixing the fluid and prior to inserting the fluid into the well shaft.
Additionally, spacer fluids containing polymerizable monomers may be used for water control and/or shut-off applications in the drilling industry. During drilling, geological formations may be encountered which allow ingress of water (for example, underground aquifers) or egress of drilling fluid (for example, cavernous formations). In either case, the addition of spacer fluids containing polymerizable monomers can seal the geological formation when applied according to the teachings of U.S. Pat. No. 6,187,839. In these cases, it would also be important to know the amount of monomer in the fluid prior to application in the well.
Several factors complicate the determination of the amount of monomer in the fluid. First, the spacer fluid is a complex mixture that has a color and consistency similar to mud. Second, the spacer fluid may be prepared on land, and subsequently shipped by boat to an off-shore drilling rig, which may take several days and be subject to weather and/or drilling schedule delays. Thus, analysis may need to occur on the boat, which requires analytical instrumentation that is robust, compact (due to space constraints), accurate and relatively simple to use. A need exists, therefore, for a method of determining the concentration of a polymerizable monomeric species in well spacer fluid which meets the aforementioned criteria.